The present invention relates to gate valves of the type having a pair of gates movable in a valve body between open and closed positions, with a wedge interposed between the gates to urge the gates against corresponding valve seats in the valve body.
Walther U.S. Pat. No. 3,695,578, and DE-AS 1 150 250 illustrate two prior art gate valves of the general type described above. In both of these gate valves, a wedge assembly made up of two wedge halves interconnected by a ball and socket joint is used to move the gates between the open and closed positions, and to provide a sealing force tending to seat the gates against the valve seats. The use of such an internal wedge assembly provides important advantages in reducing the tendency of the valve to jam in the closed position. Such jamming can result from stresses associated with temperature changes of the valve when in the closed position. The internal wedge assembly eliminates such jamming by relative movement between the internal wedge assembly and the gates. This relative movement occurs before the gates are unseated from the valve faces, and it reduces sealing forces on the gates as the gates move to the open position.
The gate valve design illustrated in the above-identified patents brings with it disadvantages due to the complex structure of the wedge assembly. The wedge assembly itself is made up of three component parts which must be assembled properly prior to the assembly of the gate valve. These multiple component parts unnecessarily increase the cost, complexity and maintenance difficulties associated with the valve. Furthermore, the three-part wedge assembly defines a large number of surfaces that may collect scale or other solid deposits which may interfere with proper operation of the valve.